The present application is related to vehicle wheel alignment measurement procedures, and in particular, to a procedure for utilizing data acquired during a vehicle wheel alignment rolling compensation procedure to detect variations in the flatness or uniformity of a surface over which the vehicle is rolling, and to compensate subsequently acquired measurements for effects of any detected surface variations.
In any vehicle wheel alignment measurement system, an orientation of an axis of rotation for each individual wheel assembly of the vehicle must be determined before alignment angles associated with the wheel assemblies can be measured or calculated. In an ideal application, angle sensors or optical targets associated with the vehicle wheel alignment system are mounted to the wheel assemblies in precise alignment with the wheel assembly axis of rotation, enabling measurements to be directly obtained. In practice, precise alignment of the sensors or targets with the wheel assembly axis of rotation is difficult to achieve due to various factors such as imperfections in the wheel assembly surfaces, improper attachment of the sensor or target, machining tolerances, etc.
While a precise alignment to within an acceptable tolerance between sensors or optical targets and the wheel assembly can be achieved through the use of highly accurate machined components and special “no-comp” mounting adapters for securing a sensor or optical target to the wheel assembly, it is not always an optimal solution. When a “no-comp” wheel adapter is mounted on the wheel assembly in a precise and determined mounting using machined provisions on either a wheel or brake hub, the axis of the wheel adapter is expected to be coaxial with the axis of rotation of the wheel assembly. A pre-compensated vehicle wheel alignment sensor or optical target is then mounted in the aligned socket of the wheel adapter, and alignment measurements are obtained without any further compensation steps. However, any damage to the wheel adapter, or foreign objects or debris present in the interface between the wheel adapter and the machined provisions on the wheel assembly or brake hub will cause erroneous readings. Furthermore, due to the precision machining required, the “no-comp” adapters are expensive components to manufacture, and must be handled with care to ensure continued accuracy.
In an alternative to using “no-comp” precision mounting adapters, a vehicle wheel alignment measurement system may identify and accommodate the reality of imperfections introduced by mounting an alignment sensor or optical target onto a wheel assembly without precise coaxial alignment to the wheel assembly axis of rotation. One such method utilizes a compensation procedure which involves observing changes in parameters associated with a wheel assembly, such as camber and/or a toe angles, measured by the vehicle wheel alignment system using the secured alignment sensor or optical target, at different rotational positions of a wheel assembly on which the alignment sensor or optical target is mounted. These rotational positions may be observed by rolling the vehicle over a flat surface for a distance sufficient to acquire the necessary measurement data. Measurement changes which are caused by any eccentricity in the mounting of each alignment sensor or optical target to the wheel assembly are identified by an observable sinusoidal pattern in the resulting measurements, enabling subsequent measurements to be suitably compensated for the observed eccentricity at any rotational position of the wheel assembly.
Deviations from level, straight-line rolling movement of the wheel assembly during the rolling compensation observations can affect the outcome of the compensation calculations. These deviations result from the vehicle being steered during the rolling movement, which alters wheel assembly orientation, or from rolling the wheel assembly over an un-level surface, such as a vehicle lift runway which is warped, bent, twisted, or which has some form of surface discontinuity, such as a gap, ridge, bump, or portions of differing elevations. Accordingly, it would be beneficial to provide a method for detecting the occurrence of some or all of these deviations during the rolling compensation observations, either to provide a warning to the operator, or to account for some or all of the deviations during the compensation calculations in order to reduce the resulting effects on the rolling compensation values.